Dispensing modules are commonly used to dispense viscous liquids, such as hot melt adhesives, in a variety of dispensing applications employed in the manufacture of products and in product packaging. Conventional dispensing modules are provided with either electrically actuated or electro-pneumatically actuated valve assemblies that regulate the flow and discharge of adhesive from the dispensing module. Typically, the valve assembly incorporates a valve element that is movable to a valve seat between open and closed positions. In the closed position, the valve member seals against the valve seat with a continuous line of contact to discontinue a flow of the adhesive from an outlet of the dispensing module. Cyclical movement of the valve element between the open and closed positions intermittently interrupts the flow to generate a pattern of adhesive on a receiving surface of the product or product packaging.
In many instances, the pattern includes one or more “beads” of the adhesive. The term “bead” generally refers to a continuous discharge of the adhesive, or any other viscous liquid, on the receiving surface with a desirable length, height, width, or other dimension. While the dimensions may vary given the particular application, the ability to repeatedly, accurately, and precisely initiate and terminate the bead provides a manufacturer with the best opportunity to efficiently position each bead on the receiving surface without waste. For example, there are many applications in which it is desirable or necessary to sharply cut off flow of the adhesive from the dispensing module to quickly and precisely terminate the bead on the receiving surface.
Unfortunately, known dispensing modules require a tradeoff between repeatability discharging adhesive and sharply cutting off the flow of adhesive. On one hand, many known dispenser modules capable of sharply cutting off the flow of adhesive tend to be more prone to “clogging,” in which the adhesive blocks the outlet from the further discharge of adhesive. Clogged dispensing modules must be manually cleaned or replaced, resulting in equipment downtime and significant labor and replacement costs to the manufacturer. On the other hand, many known dispenser modules capable of physically displacing clogged adhesive tend to be more prone to a bead “tailing effect,” in which the flow of adhesive gradually reduces to terminate the bead. The “tailing effect” refers to the bead tapering to termination due to the more gradual flow reduction. For this reason, manufacturers carefully consider these various tradeoffs when selecting a dispensing module for a particular application.
There is a need for a dispensing module and method for dispensing a viscous liquid that sharply cuts off the flow of viscous liquid and inhibits clogging while addressing issues such as those discussed above.